Phase transitions and crossovers in reaction-diffusion models with catalyst deactivation

The activity of catalytic materials is reduced during operation by several mechanisms, one of them being poisoning of catalytic sites by chemisorbed impurities or products. Here we study the effects of poisoning in two reaction-diffusion models in one-dimensional lattices with randomly distributed catalytic sites. Unimolecular and bimolecular single-species reactions are considered, without reactant input during the operation. The models show transitions between a phase with continuous decay of reactant concentration and a phase with asymptotic non-zero reactant concentration and complete poisoning of the catalyst. The transition boundary depends on the initial reactant and catalyst concentrations and on the poisoning probability. The critical system behaves as in the two-species annihilation reaction, with reactant concentration decaying as t^{-1/4} and the catalytic sites playing the role of the second species. In the unimolecular reaction, a significant crossover to the asymptotic scaling is observed even when one of those parameters is 10% far from criticality. Consequently, an effective power-law decay of concentration may persist up to long times and lead to an apparent change in the reaction kinetics. In the bimolecular single-species reaction, the critical scaling is followed by a two-dimensional rapid decay, thus two crossovers are found.Comment: 8 pages, 7 figure

Developpement d'un système de dopage "PM" : premiers essais

National audienceThe participation to inter-laboratory exercises is a key step for any ambient air quality monitoring network. To guarantee the interest of such campaigns, participants need a large range of concentration, including regulatory limits. As far as PM10 is concerned, the 1996 European directive implement a 24h hours limit of 50 micro g/m3 with a maximum relative uncertainty of 25%. In the frame of the French National Air Quality Laboratory (LCSQA), INERIS -in relation with LNI Inc.- is developing a special PM generator. The objective is to distribute to all participants an ambient air enriched with PM10 or PM2,5 particles. Preliminary results show that our prototype is able to distribute to 4 TEOM and TEOM-FDMS microbalances air in a range from the background up to 100 micro g/m3 and more. The set-up and the results will be presented.La reconnaissance d'une compétence en matière de mesurage passe par la participation à des exercices d'intercomparaison, ou " exercices inter-laboratoires ". Ce type d'exercice est organisé dans le cadre de la surveillance réglementaire " air ambiant " française. Afin de garantir l'efficacité d'une telle session, il est essentiel de bénéficier d'un spectre large de concentration, et tout particulièrement d'inclure les valeurs limites pour lesquelles il existe des exigences en matière d'incertitude. C'est le cas de la surveillance des PM10, pour lesquels une incertitude maximale de 25% est exigée à 50 micro g/m3 (mesure journalière). Il est en pratique impossible de garantir a priori un tel niveau de concentration. C'est pourquoi dans le cadre du LCSQA, l'INERIS a entrepris de développer des systèmes d'enrichissement, appelés aussi " systèmes de dopage ". La présente communication est consacrée au développement d'un tel dispositif pour les particules de type PM10 et PM 2,5. Les objectifs, le montage expérimental, ainsi que les premiers résultats, seront rapportés dans le cas de microbalances TEOM et TEOM-FDMS, pour des concentrations allant du niveau de fond à plus de 100 micro g/m3. Une attention particulière sera portée sur les contraintes et les résultats obtenus en matière de représentativité de la matrice, ainsi qu'en matière d'équivalence des échantillons fournis à chaque analyseur participant

Imaging along-strike variations in mechanical properties of the Gofar transform fault, East Pacific Rise

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 119 (2014): 7175–7194, doi:10.1002/2014JB011270.A large part of global plate motion on mid-ocean ridge transform faults (RTFs) is not accommodated as major earthquakes. When large earthquakes do occur, they often repeat quasiperiodically. We focus here on the high slip rate (∼14 cm/yr) Gofar transform fault on the equatorial East Pacific Rise. This fault is subdivided into patches that slip during Mw 5.5–6 earthquakes every 5 to 6 years. These patches are separated by rupture barriers that accommodate slip through swarms of smaller events and/or aseismic creep. We performed an imaging study to investigate which spatiotemporal variations of the fault zone properties control this segmentation in mechanical behavior and could explain the specific behavior of RTFs at the global scale. We adopt a double-difference approach in a joint inversion of active air gun shots and microseismicity recorded for 1 year. This data set includes the 2008 Mw 6 Gofar earthquake. The along-strike P wave velocity structure reveals an abrupt transition between the barrier area, characterized by a damaged fault zone of 10–20% reduced Vp and a nearly intact fault zone in the asperity area. The importance of the strength of the damage zone on the mechanical behavior is supported by the temporal S wave velocity changes which suggest increased damage within the barrier area, during the week preceding the Mw 6 earthquake. Our results support the conclusion that extended highly damaged zones are the key factor in limiting the role of major earthquakes to accommodate plate motion along RTFs.The material presented here is based on work supported by the National Science Foundation grants 1232725 and 0242117.2015-03-2

Применение уравнений Френеля в статистическом анализе эллипсометрических данных - определение оптических показателей анодно полученных плёнок из TiO2

Оптические показатели TI02 плёнок , определены эллилсометрически при стандартных ех-ситовых условиях в видимой спектральной области. Плёнки , изготовленные из Ti02, получены анодным окислением электрополирован:ной титановой поверхности в области потенциала от О до 100 V. Путём вычисления:, с помощью измеренных эллипсометрических параметров L1 и Р и Френеловых уравнений, показано , что численное значение оптических показателей уменьшае11ся: с изменением т олщины плёнки, и что у тол·стых плёнок они получают постоянные значения:. Исползован и ем различных спос обо в выч исления: пок.азано, каким образом можно получить наиболее точные рез у ль таты, т. е. самая: маленькая: погрешность при статистической обработке эллипсометрических д анных

Whistler Wave Observations by \textit{Parker Solar Probe} During Encounter 11: Counter-Propagating Whistlers Collocated with Magnetic Field Inhomogeneities and their Application to Electric Field Measurement Calibration

Observations of the young solar wind by the Parker Solar Probe (PSP) mission reveal the existence of intense plasma wave bursts with frequencies between $0.05$ -- $0.20 f_\mathrm{ce}$ (tens of Hz up to ${\sim}300$ Hz) in the spacecraft frame. The wave bursts are often collocated with inhomogeneities in the solar wind magnetic field, such as local dips in magnitude or sudden directional changes. The observed waves are identified as electromagnetic whistler waves that propagate either sunward, anti-sunward, or in counter-propagating configurations during different burst events. Being generated in the solar wind flow the waves experience significant Doppler down-shift and up-shift {of wave frequency} in the spacecraft frame for sunward and anti-sunward waves, respectively. Their peak amplitudes can be larger than $2$~nT, where such values represent up to $10\%$ of the background magnetic field during the interval of study. The amplitude is maximum for propagation parallel to the background magnetic field. We (i) evaluate the properties of these waves by reconstructing their parameters in the plasma frame, (ii) estimate the effective length of the PSP electric field antennas at whistler frequencies, and (iii) discuss the generation mechanism of these waves